1. Field of the Invention
The present invention, in general relates to electrical contacts and, more particularly, to electrical contacts that permit maximal current flow with minimal insertion force.
The pin and socket configuration of electrical contacts is common in a variety of industries and frequently includes a solid pin contact that mates to a slotted or xe2x80x9csplit tinexe2x80x9d type of a socket contact.
The split tine socket is typically deformed radially inward after machining in order to achieve an adequate normal force when mated to the pin contact. This deformation is sometimes referred to as a xe2x80x9csetxe2x80x9d.
Another method of achieving inward normal force on the pin contact is the use of a separate coil spring or xe2x80x9cCxe2x80x9d clip spring that is wrapped around the tip of the tines and which tends to urge them inward, toward the pin.
A common type of problem that occurs generally with these types of contacts involves achieving a consistent normal force. A consistent normal force results in consistent mate/unmate forces and also in a consistent, and preferably, low voltage drop across the connection.
Maintaining a consistent normal force over the life of the contact, which may be subjected to harsh environments and abuse, remains a vexing problem in the industry.
These issues are especially important when high currents are involved, such as when fast charging electric vehicles. Also, the connectors that utilize these types of contacts may be handled by personnel with limited strength.
It is desirable that such contacts have low mate and unmate forces and that those forces remain relatively constant throughout the connector""s useful service life.
If the mate/unmate force is too high, the connector, having a plurality of contacts, may be unusable by some people of limited strength. Conversely, if the contacts loosen excessively over time (i.e., if the normal force decreases substantially), a resulting increase in resistance and therefore voltage drop can occur. This, in turn, will cause a rise in temperature and may result in an unsafe situation.
Setting the tines of the contact requires using a material with a sufficiently low yield strength such that sufficient permanent deformation can take place within the constraints of the slit width, in order to achieve the desired normal force.
Unfortunately, permanent deformation in the outward radial direction or xe2x80x9clooseningxe2x80x9d can occur over the life of the contact resulting in a reduction of normal force and an increase in voltage drop. Loosening is a common problem with connectors that are mated and unmated repeatedly.
This is especially true when the connector design allows a rocking motion to be used as an aid in mating and unmating. Installing an external helper spring wrapped around the tip of the tines can help alleviate this problem because the spring is made of a high yield strength material that is resistant to permanent deformation.
However, the external spring""s spring rate, dimensions, and frictional characteristics contribute to a variation in normal force. Also, the frictional characteristics of the spring/tine interface are subject to change over the life of the contact, especially in harsh environments. Furthermore, this approach tends to increase the mate/unmate forces that are required. It also adds one more component part (i.e., the external spring) to the assembly of each contact.
Also, prior art design of contacts, especially high current contacts, has been based on the prevailing assumption that it is desirable to maximize the contact area intermediate a pin and a socket. The more contact area that occurs at the interface between the pin and the socket, it has been believed, will increase the opportunity for current to flow. It has been thought that current flow will occur at least somewhere wherever there is the potential for physical contact to occur, so the greater the potential for that contact to occur and to occur in as many places as possible, became the essence of optimum high current contact design theory.
It was further believed that a great amount of surface area for contact is absolutely necessary to support high current loading through the connector. The problem with maximizing contact area is that, for any given tine to pin pressure (i.e., normal force), a greater area for contact results in less normal force being applied at any given location. This tends to result in random spots of contact occurring. If contact is random, there is little assurance that any mechanical xe2x80x9cwipingxe2x80x9d will clean the pin and tines at the exact areas where physical contact will occur.
This, it has been found, decreases the current carrying ability of a contact over its life because oxidation that occurs is not optimally cleaned by the wiping action of the tine with the pin. Also a lower normal force also tends to increase electrical resistance in general.
Accordingly, there exists today a need for an electrical contact that is durable and reliable, adaptable for use in harsh environments, requires a minimal mate/unmate force, and is capable of carrying high currents.
2. Description of Prior Art
Electrical contacts are, in general, well known. While the structural arrangements of the known types of devices, at first appearance, may have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.
It is an object of the present invention to provide an electrical contact that lessens the mate and unmate forces that are required.
It is also an important object of the invention to provide an electrical contact that is durable.
Another object of the invention is to provide an electrical contact that increases the current carrying ability of the contact.
Still another object of the invention is to provide an electrical contact that uses the tines as springs to supply a normal force.
Still yet another object of the invention is to provide an electrical contact that is adapted to distribute stress along its longitudinal length.
Yet another important object of the invention is to provide an electrical contact that includes limited areas, or patches, of physical contact intermediate a pin and tine.
A still further object of the invention is to provide an electrical contact that includes predictable areas of physical contact to occur intermediate a pin and tine.
A still further important object of the invention is to provide an electrical contact that provides a wiping action of the tine upon the pin which tends to clean that specific area of the pin with each mating/unmating cycle.
Still yet another important object of the invention is to provide an electrical contact that includes a reverse taper of a portion of a tine.
Still yet one further object of the invention is to provide an electrical contact that includes a two-stage tine.
Still yet one further important object of the invention is to provide an electrical contact that includes a socket with at least one tine that has a first inside radius and a pin that has a second outside radius where the outside radius of the pin is greater than the first inside radius of the tine, which results in contact occurring intermediate the tine and the pin longitudinally along a portion of the inside edge of each tine.
Still one further valuable object of the invention is to provide an electrical contact that includes tines, at least a portion of which are formed of a high yield strength type of conducting metal.
Briefly, an electrical contact that is constructed in accordance with the principles of the present invention has a split tine socket that is machined out of a high yield strength conducting metal such that neither tine setting nor external helper springs are required. Each tine acts as a two-stage spring and includes a first stage that is thicker near the base of the tine and a second stage that is thinner and which continues away from the base to the tip of the tine. The first stage adds compliance to side loads inflicted by the pin tip when a rocking motion is used to mate the connectors, thereby protecting the socket from permanent deformation or loosening. The outside diameter of the tines is tapered such that when a pin contact is mated, the outside profile becomes nearly cylindrical which maintains a minimal clearance to the inside diameter of a metallic hood which, in turn, constrains the tines and prevents them from loosening by being bent beyond their elastic limit. The inside diameter of the second stage tine is machined with a reverse taper which ensures contact primarily at the tip section of the tine which, in turn, utilizes the entire length of the tine as a spring member and allows higher normal forces, and early establishment of electrical contact integrity during mating and unmating. The distance the tip of the tine moves in and out (radially) during mating is relatively large for any given size of the contact which helps ensure that the normal forces will remain relatively constant regardless of variations that occur in the pin and socket diameters during machining and also due to dimensional changes that are caused by wear. The contact tines are designed so that contact with a mated pin occurs primarily at the tip and along a portion of the longitudinal length at the two inside edges of each tine. The arc on the inside surface of each tine has a smaller radius than the pin and therefore ensures that contact is made along the inside edges of the tine. This provides two deliberate, and relatively high pressure, contact patches that, in turn, provide optimum lines of current flow and which also serve to wipe the contacting surfaces (i.e., the contact patches) during mating and unmating to remove oxides and therefore to help maintain a low contact resistance.